A connection of this type is known in particular from the document U.S. Pat. No. 3,572,779, which describes a connection accessory formed of two parts crimped to the respective ends of two pipes; these two parts can be fastened to each other or screwed to each other.
Also known is the document WO-82/02755, which discloses an accessory including a sleeve intended to be crimped to the end of a first pipe and a fitting adapted to establish a connection with a complementary fitting mounted at the end of another pipe; in the above document this sleeve and this fitting have different hardness (or ductility) properties, i.e. the sleeve is sufficiently ductile to enable fixing by crimping whereas the fitting is sufficiently hard to locate effectively against the complementary fitting to obtain a good seal. The above document proposes a number of options for obtaining this difference in mechanical properties, including softening the sleeve part of a component initially having the hardness required for the fitting or hardening the fitting part of a component initially having the ductility required for the sleeve.
In practice the sleeve is crimped to the outside of the end of the pipe to be connected and the geometry of the exterior surface of the sleeve resists pulling out from this end (for example thanks to a longitudinal profile including a concave portion and a convex part) and rotation relative to that end (for example by means of flats).
However, the enhanced performance required of such connection accessories leads to an ongoing search for improvements, notably with regard to preventing rotation of the accessory relative to the pipe. It should be noted here that, if the accessory is used for a screwed connection, there is a risk of any rotation of one of the fittings relative to the other fitting degrading the quality of the crimp.
There is therefore a need to develop a pipe connection accessory (or connector, for short) that has, under given crimping conditions vis-à-vis a given pipe, improved resistance to rotational separation of the sleeve and the pipe.
There are various ways to achieve this.
Thus increasing the number of raised and recessed portions on the sleeve part may be considered, for improved fastening. However, as in the document cited above this sleeve is made from a ductile material, it follows that these raised and hollow portions are deformed during crimping; thus the raised portions are blunted, which minimizes the fastening effect of the raised and recessed portions. The increased resistance to rotational separation obtained in this way is therefore somewhat modest.
Increasing the amplitude of the corrugations between the concave and convex portions is not very effective either, given that the material constituting the connector is often subject to only a small amount of work hardening, especially if that material is aluminum for reasons of lightness, with the result that increasing the crimping force does not greatly increase the radial pressure between the pipe and the connector; to the contrary, such corrugations can degrade the fatigue resistance of the connector.
Depositing fixed abrasive particles on the surface of the sleeve that is intended to be crimped to the end of the pipe (or alternatively to its interior) may also be considered. However, if such particles are sufficiently hard not to be crushed during crimping, their hardness has the drawback that there is a risk of them causing cracks in the sleeve or in the end of the pipe, which seriously degrades fatigue performance.
In fact, the variety of options for adapting the connectors to improve resistance to rotation after crimping is restricted by the fact that in practice there is a requirement not to modify the conditions for fitting such connectors (or at least not to modify them significantly); these conditions are already sometimes very constraining, notably from the point of view of the accessibility of the pipes, which would appear to rule out further complicating the connector crimping conditions.